Low time-jitter single-photon detection system and method and method for satellite laser ranging

Abstract

The application discloses a kind of low time jitter single-photon detection systems and methods and satellite laser ranging method, comprising: input light module, high voltage bias module, detection chip, temperature control module, passive gate quenching circuit module, output delay measurement module, constant ratio timing module and time compensation module.The technical scheme of the present application integrates the output delay measurement technology, time compensation technology, constant ratio timing technology and semiconductor patch refrigeration technology on the basis of conventional APD, integrates the above functions, modularization, solves the time jitter problem caused by the non-constant characteristics of APD bias voltage in passive gate circuit, improves the ranging accuracy of system.At the same time, the detection system is small and exquisite, and has strong compatibility and is easy to install.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection, in particular to a low time jitter single photon detection system and method and a satellite laser ranging method. BACKGROUND

[0002] Technical term: laser ranging: laser ranging is mainly realized based on the time-of-flight principle. According to different implementation manners, it can be divided into two kinds of direct time-of-flight measurement and indirect time-of-flight measurement. Direct time-of-flight ranging is to obtain the distance information of the target by measuring the time-of-flight of the laser pulse to and fro the target; indirect time-of-flight ranging can be divided into linear frequency modulation laser ranging, phase laser ranging and amplitude modulation laser ranging according to different implementation methods. In addition, according to different observation targets, laser ranging can be divided into satellite laser ranging (SLR), space debris laser ranging (DLR) and lunar laser ranging (LLR) and the like.

[0003] Single photon detector: an ultra-sensitive photoelectric detector that responds to a single photon signal and converts it into a macroscopic electrical signal output.

[0004] Avalanche voltage: the voltage threshold of the two working modes of APD. Just when the APD occurs avalanche greater than gain, the bias voltage value applied to its two ends is called avalanche voltage Vb. When the reverse bias voltage across the APD is less than the avalanche voltage, the gain of the APD output current is far from enough. Only when the reverse bias voltage is greater than the avalanche voltage, the number of carriers in the APD increases exponentially, so that a photon energy can be amplified and detected. Generally speaking, the size of the avalanche voltage is related to the ambient temperature of the APD device. The lower the ambient temperature, the lower the avalanche voltage.

[0005] Time jitter: refers to the time difference between the output electrical signal of the detector and its response to the incident photon signal. Time jitter is related to the avalanche characteristics of the APD and the response characteristics of the APD detection circuit. Although the peripheral circuit of the APD can also produce a large time jitter, for the APD itself, the main factors that produce jitter include the absorption position of the photon in the absorption region, the transmission time of the carrier at the interlayer interface (especially the time of the transition region hole being captured-released), and the establishment time of the avalanche amplitude reaching the discrimination level.

[0006] Response time: The time it takes for the photocurrent to rise to a steady value corresponding to the incident light power after a short light pulse is incident on the detector. The response time t is usually used to describe the detector's need for a pulsed form of incident light. The time constant t is usually determined by three factors: 1) the time delay due to carrier diffusion 2) the time delay due to carrier drift in the depletion layer. As the depletion layer narrows, the carrier drift time decreases, and the absorption coefficient of the photons also decreases, resulting in a decrease in responsivity. 3) the depletion layer capacitance. The narrower the depletion layer, the greater the depletion layer capacitance, thus increasing the time constant, and therefore the appropriate depletion layer width should be chosen. 4) In addition, the material, structure and peripheral circuit of the detector will also determine the size of the response time t.

[0007] Postpulse: In a diode, part of the electrons (holes) excited by photons are captured by the lattice defects or impurities of the semiconductor material, which re-induce the avalanche gain consistent with the original photo-generated electrons (holes), which is called postpulse. Correspondingly, the probability of the diode generating a pulse when there is no new photon irradiation is the postpulse probability. In actual measurement, it is very important to reduce the postpulse probability to a low level. Improving the crystal quality of the semiconductor material can effectively suppress the postpulse effect, for example, significantly reducing the defect density. In addition, reducing the number of photo-generated carriers or shortening the lifetime of trapped carriers can also reduce the postpulse during the avalanche process.

[0008] Dark count: Refers to the count rate of the detector without incident light signal. It is usually caused by the thermal motion of carriers due to the lattice defects of the APD material itself. The internal carrier motion can be reduced by cooling the APD to a low temperature state through a cooling module, thereby reducing the dark count.

[0009] Detection efficiency: The ratio of the number of electron-hole pairs excited by the APD to the number of incident photons is defined as the detection efficiency. In other words, it is the probability that the detector receives a photon to generate a macroscopic electrical signal, which is used to measure the photoelectric conversion capability of a single-photon detector. The size of the detection efficiency is related to three aspects: the coupling probability of the photon and the detector, the generation probability of the electron-hole pair and the avalanche probability.

[0010] Dead time: The time interval during which the APD cannot respond to the second photon after detecting the first photon is defined as the dead time. The dead time limits the maximum photon count rate at which the detector can work. The maximum count rate of different light detectors ranges from kHz to MhZ. Therefore, the dead time is mainly determined by the type of detector, but the value of the measured dead time is usually determined by the detector and its peripheral circuit together.

[0011] Background: High-precision time interval measurement system is an important research means in many fields such as modern astronomical observation, high-energy physics experiment, satellite navigation, time comparison, quantum communication, geodetic survey, laser ranging and other aspects of time measurement and time synchronization, which has important military value and economic significance. The most critical technology is the accurate determination of the arrival time of laser pulses. The emergence of single photon detector has improved the sensitivity of time interval measurement system to single photon or few photon level, which opens up new technical potential for the development and application of time interval measurement system. As the core module of high-precision time interval measurement technology, its detection performance plays a key role in the time interval measurement system.

[0012] There are many kinds of single photon detectors at present, including PMT, SPAD, SNSPD, APD, etc. Among them, PMT has the advantages of high gain, large photosensitive surface and low dark count, but PMT has the disadvantages of large volume, low quantum efficiency, high reverse bias, weak resistance to external magnetic field, which is not conducive to array expansion. The application in the field with high integration requirement is limited. SNSPD as a new single photon detector, has the advantages of wide spectrum, extremely low dark count, low time jitter, short recovery time and no need for gate circuit, etc., and has important application in quantum optics and astronomical observation, but the low temperature working environment of 4k seriously limits its expansion to application field. In contrast, APD has the advantages of large gain, fast response speed, high detection efficiency, small volume, easy to array integration, low power consumption, no need for ultra-low temperature environment, etc., and has become the best choice for practical single photon detector.

[0013] As Figure 1As shown, a complete single photon detection system includes a bias circuit part of the device, an APD chip part, a temperature control part, and a signal detection part. The bias circuit part provides the necessary condition for the avalanche: a bias voltage Vbreak greater than the avalanche breakdown voltage, which is the superposition of a direct current voltage slightly less than the APD breakdown voltage and a pulse voltage. The temperature control part provides the necessary low temperature environment for the APD, and the working temperature of the APD is generally about -50°C. A semiconductor thermoelectric cooling device is generally used to cool the APD to this temperature, and a temperature control device is used to stabilize the temperature within a range of ±1°C. The signal detection part mainly includes a spike noise suppression circuit, an avalanche signal discrimination circuit, and a counting circuit, and the purpose is to improve the single photon avalanche signal and record the results. The working mechanism of the APD is that a reverse bias higher than the avalanche voltage Vbreak is applied across the APD, and under this bias, a single charge carrier injected into the depletion layer can trigger a self-sustaining avalanche, and the current rises rapidly to a stable value of milliamperes. If the initial charge carrier is generated by light, the rising edge of the avalanche current represents the arrival time of the detected light signal, and the accuracy can reach the picosecond level. When the bias across the detector is lowered below Vbreak, the avalanche ionization is quenched. In order to detect the next photon, the detector bias must be returned to a state higher than Vbreak.

[0014] In a high-precision time interval measurement system, the time jitter of the APD directly affects the resolution and accuracy of the measurement. The time jitter refers to the uncertainty between the time when the macroscopic avalanche of the APD is detected and the time when the incident light arrives, which is related to the avalanche characteristics of the APD and the response characteristics of the APD detection circuit. To measure the time jitter, the same incident photon is measured multiple times, and the statistical distribution curve of the output signal on the time axis is obtained. The full width at half maximum (FWHM) of the curve is used to measure the time jitter of the output signal. The response time jitter of a typical single photon detector is shown in Figure 2 .

[0015] As shown in Figure 2 , the APD time jitter curve is fitted by a spike and a long tail. The spike is the time response of the charge carriers in the depletion layer, and the long tail is the time response of the neutral zone charge carriers. The smaller the time jitter, the higher the time resolution and accuracy of the detector. For the APD, the reverse bias of the device directly affects the size of the time jitter. As the reverse bias of the APD increases, the built-in electric field strength increases, the avalanche gain increases, the number of avalanche charge carriers triggered by the charge carriers increases, and the electric field strength makes the avalanche establishment time faster, thereby reducing the time jitter and greatly improving the detection efficiency. At the same time, the reliability and stability of the device degrade significantly due to the long-term operation in the high reverse avalanche current mode.

[0016] In the Geiger mode of the test condition, after the photon trigger generates avalanche current and is detected, the peripheral current should be used immediately to quench the avalanche current. The function of the quenching circuit is to quickly detect the avalanche current and extract a standard digital pulse signal, at the same time, restore the APD to a static state or cutoff mode, and wait for a new round of test state. The performance of the quenching circuit directly affects the time jitter characteristics, detection efficiency and stability of the device and other key technical indicators.

[0017] Prior art 1: The peripheral driving circuit of the APD controls the bias voltage across the detector to ensure that the device completes the entire detection process continuously, quickly and stably. Passive quenching is the most basic near-infrared APD avalanche quenching method, and its principle is as follows Figure 3The APD is in series with a high impedance quenching resistor R1. The breakdown voltage of the APD is Vbr, the excess voltage is Vex, and the actual voltage applied to the APD is Vbr+Vex. The APD mainly experiences a preparation stage, an avalanche stage, and a recovery stage during detection. Preparation stage: In this stage, there is no working illumination on the APD, and theoretically there is no avalanche current. The impedance of the quenching resistor R1 is very large, but it can still be ignored compared with the impedance of the reverse APD. The voltage obtained by the APD is the entire reverse bias voltage, so the APD is in the Geiger mode, ready to receive photons and trigger the avalanche gain process. Obviously, this stage is the long-time state of the APD. Avalanche stage: In this stage, the photons are illuminated on the APD, generating photo-generated carriers that undergo avalanche gain process under the action of ionization effect, and the avalanche current increases rapidly. According to the voltage division principle, the voltage divided by the quenching resistor R1 increases, and the working voltage applied to the APD decreases rapidly to below the avalanche voltage, completing the quenching of the avalanche signal. Recovery stage: Since the APD has a junction capacitance, after the avalanche ends, the APD needs a charging recovery stage to return to the Geiger mode. The bias voltage charging time constant Tr of the APD is. Obviously, the charging and discharging time of the APD is related to the quenching resistor R1. Generally, it is in the order of microseconds. In the recovery stage, the APD cannot work, but the photons reaching the APD will also have an avalanche signal, only the amplitude is smaller. Therefore, the more fully the APD recovers, the higher the amplitude of the next avalanche signal, and the smaller the probability of after-pulse. Overall, the passive quenching circuit has a simple structure, but the dead time is long and the detection rate is low. The disadvantages are: the passive quenching method is the simplest among all quenching methods, only a large resistance of 100kΩ or more is needed in series, and the automatic quenching is realized by the current limiting and voltage dividing effect of the resistance. However, in the passive quenching circuit, the reverse bias voltage applied to the APD is too long, and the quenching time is in the order of 100ns, and the quenching process is too slow, which seriously limits the detection rate of the APD. Moreover, the device is in a long-term avalanche current mode under high reverse bias, and the reliability and stability of the device degrade obviously. In addition, the high resistance resistor will occupy a large area of the layout, which is not conducive to device integration.

[0018] Prior art 2: Unlike passive quenching circuit, the main feature of active quenching circuit is to add a positive feedback loop in the loop. Active quenching method adopts a low resistance Rs in series with APD to reduce the bias voltage for quenching. The specific process is: after the avalanche excitation, the avalanche current will generate a large voltage on the detection resistor Rs, at this time the rear-end comparator will detect the jump of the signal, and then generate a high level pulse, and the generated high level will trigger the active quenching switch to reduce the reverse bias voltage of APD to less than the breakdown voltage value, and complete the quenching of APD. The active quenching circuit makes the bias voltage of APD less than the avalanche breakdown voltage, so its quenching time is very fast. The disadvantage is: compared with passive quenching, the quenching and recovery time of active quenching circuit depends entirely on the speed of the comparator and is not limited by the RC charging and discharging theory, which can realize fast quenching and resetting, thus reducing the dead time and the influence of after-pulse, which is beneficial to realize fast imaging. However, due to the use of high-speed comparator in the circuit, the over-bias voltage loaded on the APD is not more than 5V, which limits the size of APD avalanche gain and device detection efficiency. In addition, due to the introduction of feedback loop in the active quenching circuit, the circuit area inevitably increases, and the timing is relatively complex, and the circuit power consumption is much higher than that of passive quenching circuit, as shown in Figure 4 .

[0019] Prior art 3: Gated quenching circuit is the most common quenching circuit in laser ranging system, which needs additional input of gating signal "on" and pre-charging signal "off". For passive quenching and active quenching, APD devices are always in working state, which inevitably suffers from dark count and after-pulse, reducing the detection efficiency. To solve this problem, gated quenching circuit sets a gating window signal to enable quenching current, so that it only detects photons within the window. When the window signal "on" is invalid, the anode of APD is pre-charged to high potential, and the device is in high impedance state, which cannot occur avalanche breakdown, thereby effectively avoiding the influence of dark count and after-pulse. Compared with passive quenching, the response speed of gated quenching current is faster, and the detection efficiency is higher; compared with active quenching, the quenching area is smaller, and the structure is relatively simple.

[0020] In the gated quenching circuit, as shown in Figure 5 , since the generation of dark count in the gate-on time obeys Poisson distribution, reducing the gate width as much as possible can significantly reduce the dark count. But the gate width of the gate signal is reduced to the amplitude sufficient to suppress the avalanche pulse that may occur at any time in the gate, and only the safe and stable working of the APD after the quenching and recovery of the APD by the gate signal can the so-called gated passive quenching circuit be used. This circuit is based on passive circuit, and a direct current V b is loaded on APD through current limiting resistor RL, and V b is less than breakdown voltage V br , and the coupling capacitor Cc The frequency is fg, the pulse width is τg, and the amplitude is V g When the gate signal is high, the voltage applied to the APD is higher than the breakdown voltage V br APD can detect single photons, regardless of whether avalanche occurs. After τg, the gate signal becomes low, the voltage applied to the APD is lower than the breakdown voltage, and single photons cannot be detected. If the avalanche current has been established before, it will be quenched at this time. The avalanche current flows through the current-sense resistor R0 and outputs an avalanche voltage pulse. Its disadvantages are: the high-voltage capacitor C in the gate quenching circuit c It plays a vital role. It cooperates with the gate signal to arbitrarily raise or lower the potential of the APD cathode. Its main principle is as follows: when there is no avalanche event in the APD, its resistance can usually reach more than 1010Ω. At this time, the APD is approximately regarded as a high-resistance state, and the current flowing through the APD is very small. In extreme cases, the APD can be regarded as an open circuit. At the beginning of the system operation, V g It is always at a low level, and the voltage difference between the two ends of the high-voltage capacitor Cc is V b (slightly lower than the avalanche laser voltage Vbr), the potential of the APD cathode is V b When V g When the rising edge arrives, the high voltage capacitor C c The potential on the left side is raised to a high level. Since the voltage difference across the capacitor cannot change suddenly, the potential on the right side of the high-voltage capacitor C is raised to V b +V g , this voltage is higher than the avalanche voltage V br . Then V g The high level of will last for a short period of time, which is the time when the gate is open. Generally, it will not be too long because during this period, even if the APD does not have an avalanche event, the capacitor C c It will also discharge through the quenching resistor RL. If the gate is open for a long time, the potential of the APD cathode will eventually return to V b For an ideal gated quenching circuit, the gate signal and the optical signal need to be synchronized. However, in laser ranging, the actual arrival time of the optical signal has a certain deviation from the predicted time. The optical signal and the gate signal are not completely synchronized and have a certain degree of randomness. Figure 6 As shown in the figure, the APD cathode potential cannot maintain a constant value during the gate time. In other words, in a gated passive circuit, when an optical signal is incident on the APD, the reverse breakdown voltage applied to both ends of the APD is different, causing significant changes in the waveform and amplitude of the APD output pulse echo signal. This increases the timing jitter of the APD output signal, seriously affecting the system's ranging accuracy.

[0021] In summary, how to retain the high reverse bias advantage of the gated passive quenching circuit, while solving the time jitter problem caused by the non-constant inherent characteristics of the reverse bias voltage in the conventional passive quenching circuit within the width of the gating signal, is a problem that needs to be solved by the technical personnel in the field. SUMMARY

[0022] The main purpose of the embodiment of the present application is to provide a low time jitter single photon detection system, which aims to retain the high reverse bias advantage of the gated passive quenching circuit, while also solving the time jitter problem caused by the non-constant inherent characteristics of the reverse bias voltage in the conventional passive quenching circuit within the width of the gating signal.

[0023] The technical solution of the present application to solve the above technical problems is to provide a low time jitter single photon detection system, comprising:

[0024] An input optical module is used to output single photon level measured light to a detection chip;

[0025] A high voltage bias module is used to apply a reverse bias voltage to the detection chip;

[0026] A detection chip is used to receive an incident light signal and convert it into a current signal;

[0027] A temperature control module is used to maintain the working temperature of the detection chip constant;

[0028] A passive gated quenching circuit module is used to quench the avalanche pulse signal generated by the detection chip and restore the bias voltage across the detection chip;

[0029] An output delay measurement module is used to measure the detection delay Δt of the avalanche pulse signal and the "standard" avalanche pulse signal;

[0030] A constant ratio timing module is used to identify the echo time and eliminate the echo jitter caused by different signal amplitudes; and

[0031] A time compensation module is used to compensate for the drift error caused by the detection delay Δt and output the compensated echo reception time.

[0032] In an embodiment of the present application, the passive gating circuit module quenches the avalanche signal of the detection chip through a passive circuit, and restores the bias voltage across the detection chip through a gating circuit. The passive quenching is achieved by automatic quenching through high impedance suppression resistance voltage division; the gating circuit uses a set gating window signal to restore the reverse bias voltage across the detection chip.

[0033] In an embodiment of the present application, the output delay module measures the rising edge time of the avalanche pulse signal by a double-threshold front edge recognition technology, compares it with a "standard" avalanche pulse signal, acquires the current pulse output detection delay △t, and sends the delay △t to the time compensation module.

[0034] In an embodiment of the present application, the time compensation module converts a 1 ps positive pulse detection delay into a 6 ps negative time shift by assuming that the pulse detection delay △t and the time jitter difference △tjitter are in a linear relationship, acquires the time jitter △tjitter caused by the change of the pulse waveform to be detected, automatically corrects t2, accurately compensates the delay drift error caused by the non-constant reverse bias voltage within the gate signal width, and finally outputs the corrected echo signal.

[0035] To solve the above technical problems, the present application further provides a low-time-jitter single-photon detection method, which comprises the following steps:

[0036] The input light module is used for outputting the single-photon-level measured light to the detection chip, and the electron in the valence band absorbs the photon energy to jump to the conduction band, and the avalanche multiplication occurs under the action of the applied reverse bias, forming an avalanche current.

[0037] The high-voltage bias module provides a reverse bias voltage V0 slightly lower than the avalanche voltage for the APD, and at t1, the sum of the amplitude voltage V1 of the gate pulse signal provided by the passive gate quenching circuit module and the bias voltage V0 is greater than the avalanche voltage V' of the detection chip, at this time, the gate is opened, the APD is in the Geiger mode, and is used for detecting the single-photon signal.

[0038] The passive gate quenching circuit module quenches the avalanche signal of the detection chip through a passive circuit, and the gate circuit restores the bias voltage across the detection chip; the passive quenching is realized by automatic quenching through high-impedance suppression resistance voltage division; the gate circuit restores the reverse bias voltage across the detection chip by setting a gate window signal.

[0039] The output delay module measures the rising edge time of the avalanche pulse signal by a double-threshold front edge recognition technology, compares it with a "standard" avalanche pulse signal, acquires the current pulse output detection delay △t, and sends the delay △t to the time compensation module;

[0040] The constant ratio timing module dynamically adjusts the high and low levels according to the amplitude of the measured signal, takes the fixed proportional point of the signal rising edge as the time discrimination point t2, and effectively reduces the drift error of the time discrimination;

[0041] The time compensation module acquires time jitter caused by the change of the pulse waveform to be measured according to the relationship between the pulse output detection delay and the time jitter, and corrects t2 to accurately compensate the delay drift error caused by the non-constant reverse bias voltage within the width of the gate signal.

[0042] The temperature compensation module uses the semiconductor refrigeration technology to place the APD in a constant temperature environment below room temperature, ensures the stable work of the APD chip, and reduces the dark count.

[0043] To solve the above technical problems, the application further provides a satellite laser ranging method, which comprises the following steps:

[0044] Downloading the observation target prediction ephemeris of the day, selecting the observation target, and obtaining the azimuth, elevation and distance of the target satellite and other information;

[0045] The telescope is guided by the servo control system to track the target satellite, and the laser pulse is emitted after stable tracking;

[0046] The synchronization signal of the laser pulse generated by the photodiode is transmitted to the constant ratio discriminator and the main wave signal is output into the time timer A channel, and the control system records the main wave time;

[0047] The photons reflected from the target satellite are converged to the low time jitter APD target surface through the receiving telescope, and the echo signal is generated, and the echo signal is transmitted to the time timer B channel, the echo time is recorded, and the difference between the main wave time and the echo time is the distance between the satellite and the ground;

[0048] The photons reflected from the target satellite are converged to the low time jitter APD target surface through the receiving telescope, and the echo signal is generated, and the echo signal is transmitted to the time timer B channel, the echo time is recorded, and the difference between the main wave time and the echo time is the distance between the satellite and the ground;

[0049] The technical scheme of the application integrates the output delay measurement technology, the time compensation technology, the constant ratio timing technology and the semiconductor patch refrigeration technology on the basis of the conventional APD, integrates the above functions, and solves the time jitter problem caused by the non-constant characteristics of the APD bias voltage in the passive gate circuit, and improves the system ranging accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or the prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of the shown structures.

[0051] Figure 1 Structure diagram of a SPAD in the prior art;

[0052] Figure 2 Photon-to-time distribution diagram and APD time jitter in the prior art;

[0053] Figure 3 Principle diagram of a passive quenching circuit in the prior art;

[0054] Figure 4 Principle diagram of an active quenching circuit in the prior art;

[0055] Figure 5 Principle diagram of a gated quenching circuit in the prior art;

[0056] Figure 6 APD cathode potential change diagram in the prior art;

[0057] Figure 7 Structure diagram of a low-time-jitter single-photon detection system in the present application;

[0058] Figure 8 Structure diagram of a passive gated quenching circuit with low-time-jitter APD in the present application;

[0059] Figure 9 Numerical simulation curve of APD voltage change between two ends in a gated time in the present application;

[0060] Figure 10 APD avalanche pulse signal output detection delay and time jitter relationship diagram under different over-bias voltages in the present application;

[0061] Figure 11 Structure diagram of a low-time-jitter compensation APD working process in the present application;

[0062] Figure 12 Semiconductor cooling fin in the present application;

[0063] Figure 13 Laser ranging structure diagram of a low-time-jitter single-photon detection system in the present application;

[0064] Figure 14Numerical simulation diagram of APD output pulse signal under different over-bias of the present application;

[0065] Figure 15 IV curve diagram of InGaAsP / InP APD of the present application.

[0066] Explanation of reference numerals:

[0067] Label Name Label Name 1 High voltage bias module 5 Passive gating quenching circuit module 2 Input light module 6 Output delay measurement module 3 Probe chip 7 Constant ratio timing module 4 Temperature control module 8 Time compensation module DETAILED DESCRIPTION

[0068] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0069] It should be noted that all directionality indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directionality indications also change accordingly.

[0070] In addition, the description such as “first”, “second” and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as “first”, “second” can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of “several”, “a plurality of” is at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0071] In the present application, unless otherwise explicitly specified and limited, the terms “connection”, “fixation” and the like should be understood in a broad sense, for example, “fixation” can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0072] In addition, the technical solutions of each embodiment of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor is it within the protection scope claimed by the present application.

[0073] The application provides a low-time-jitter single-photon detection system, which aims to retain the high reverse bias voltage advantage of a gated passive quenching circuit and solve the time jitter problem caused by the non-constant characteristic of the reverse bias voltage in the range of the width of the gating signal in a conventional passive quenching circuit.

[0074] The specific structure of the low-time-jitter single-photon detection system will be described in the specific embodiments.

[0075] In the technical scheme of the embodiment, as shown in the figure, Figure 7 The low-time-jitter single-photon detection system comprises:

[0076] The input optical module 2 is used for outputting single-photon-level measured light to the detection chip 3.

[0077] The high-voltage bias module 1 is used for applying a reverse bias voltage to the detection chip 3.

[0078] The detection chip 3 is used for receiving an incident light signal and converting it into a current signal.

[0079] The temperature control module 4 is used for keeping the working temperature of the detection chip 3 constant.

[0080] The passive gating quenching circuit module 5 is used for quenching the avalanche pulse signal generated by the detection chip 3 and restoring the bias voltage across the detection chip 3.

[0081] The output delay measurement module 6 is used for measuring the detection delay Δt of the avalanche pulse signal and a "standard" avalanche pulse signal.

[0082] The constant-ratio timing module 7 is used for discriminating the echo time and eliminating the echo jitter caused by different signal amplitudes.

[0083] The time compensation module 8 is used for compensating the drift error caused by the detection delay Δt and outputting the compensated echo receiving time.

[0084] It can be understood that the application integrates the output delay measurement technology, the time compensation technology, the constant-ratio timing technology and the semiconductor patch refrigeration technology on the basis of the conventional APD, integrates the above functions, and solves the time jitter problem caused by the non-constant characteristic of the APD bias voltage in the passive gating circuit, thereby improving the system ranging accuracy. Meanwhile, the detection system is small in size, strong in compatibility and easy to install.

[0085] In a feasible embodiment, the detection chip 3 is an InGaAsP InP APD chip.

[0086] In one embodiment of the present invention, the passive gating circuit module quenches the avalanche signal of the detection chip 3 through a passive circuit, and restores the bias voltage at both ends of the detection chip 3 through a gating circuit. Passive quenching is achieved automatically by high-impedance suppression resistor voltage division; the gating circuit uses a set gating window signal to restore the reverse bias voltage at both ends of the detection chip 3.

[0087] It can be understood that the passive gate control circuit module adopts the passive gate control quenching circuit technology, such as Figure 8 As shown in Figure 1, this circuit can not only load a high reverse bias voltage on the APD, but also minimize the interference of background noise. However, for conventional passive gated quenching circuits, the bias voltages loaded on the left and right ends of the APD when avalanche occurs have non-fixed characteristics; Figure 9 As shown in the figure, the specific process is as follows: When no avalanche event occurs in the APD, the APD is approximately regarded as a high-resistance state, and the bias voltage across the APD is -80V; the potential of the APD cathode is 20V, and the voltage difference across the high-voltage capacitor C1 is 100V; when the gate signal arrives, the potential on the left side of C1 rises to 0V. Since the voltage difference across the capacitor cannot change suddenly, the potential on the right side of the high-voltage capacitor C rises to -100V, which is higher than the APD avalanche voltage of 83V, and the APD enters the "ready" state. When a photon enters the APD chip during the gate time, it will trigger an avalanche in the device. It is worth noting that the high level across the APD is not constant during the gate time, and the capacitor C1 will discharge through the quenching resistor RL.

[0088] In one embodiment of the present invention, the output delay module measures the rising edge time of the avalanche pulse signal through a dual-threshold leading edge recognition technology, compares it with the "standard" avalanche pulse signal, obtains the current pulse output detection delay △t, and sends the delay amount △t to the time compensation module 8.

[0089] It can be understood that the output delay module uses numerical simulation technology to obtain the rise delay time and time jitter of the avalanche pulse under different over-bias voltages. The results are as follows Figure 10 As shown, based on Figure 10According to the numerical simulation results shown in the figure, in the output delay module, the double-threshold front edge identification technology is adopted, the 10% and 90% of the amplitude of the avalanche pulse signal are timed by the comparators and the timer, the rising edge time of the avalanche pulse signal is obtained, and the current pulse output detection delay △t is obtained by comparing with the "standard" avalanche pulse signal, the two comparators are used, and the delay amount △t is sent to the time compensation module 8. Then, in the constant ratio timing module 7, the comparator threshold voltage is dynamically adjusted according to the input pulse signal amplitude, the two signals are compared by using the high-speed comparator, and the time point when the voltage values of the two signals are equal is selected as the timing point, one of the two signals is a pulse signal with a small delay, and the other is the decay signal of the pulse signal. When the pulse signal shape is unchanged, the fixed proportional point of the signal rising edge is used as the time point discrimination point, the time jitter error caused by the amplitude change is reduced, and the time discrimination t2 accuracy is improved. Finally, in the time compensation module 8, the 1ps positive pulse detection delay is converted into 5ps negative time shift by using the high-speed comparator and the amplifier, the t2 time is automatically corrected, the delay drift error caused by the non-constant reverse bias voltage in the gate signal width is accurately compensated, and the corrected echo signal is output to the time timer B channel. The specific process is as Figure 11

[0090] In an embodiment of the application, the time compensation module 8 converts the 1ps positive pulse detection delay into 6ps negative time shift by assuming that the pulse detection delay △t and the time jitter difference △tjitter are in a linear relationship, obtains the time jitter △tjitter caused by the change of the pulse waveform to be measured, automatically corrects t2, accurately compensates the delay drift error caused by the non-constant reverse bias voltage in the gate signal width, and finally outputs the corrected echo signal.

[0091] In a feasible implementation, the time compensation module 8 uses the FPGA to fine-tune the avalanche discrimination time t2 according to the pulse detection delay △t by table lookup, accurately compensates the delay drift caused by the non-constant reverse bias voltage, and realizes the delay stability of the detector output.

[0092] In a feasible implementation, the temperature compensation module uses the semiconductor refrigeration technology to ensure the working temperature of the APD; the semiconductor refrigeration technology only needs to change the current size or the power-on time to control the size of the refrigeration amount, the cooling speed is faster and controllable; effectively improves the stability of the system, also makes the system structure more compact, is conducive to the further integration and application of the system; the structure of the semiconductor refrigeration sheet is as Figure 12

[0093] To solve the above technical problems, the application further provides a low-time-jitter single-photon detection method, which comprises the following steps: ​​

[0094] S10: The input light module is used for outputting single-photon level measured light to a detection chip, and the valence band electron absorbs photon energy to jump to the conduction band, and avalanche multiplication occurs under the action of an applied reverse bias, thereby forming an avalanche current;

[0095] S20: The high-voltage bias module provides a reverse bias voltage V0 slightly lower than the avalanche voltage for the APD, and at t1, the sum of the amplitude voltage V1 of the gate pulse signal provided by the passive gate quenching circuit module and the bias voltage V0 is greater than the avalanche voltage V' of the detection chip, at this time, the gate is opened, the APD is in the Geiger mode, and is used for detecting single-photon signals;

[0096] S30: The passive gate quenching circuit module quenches the avalanche signal of the detection chip through a passive circuit, and the gate circuit restores the bias voltage across the detection chip; passive quenching is achieved by high-impedance suppression resistance voltage division, and has the advantages of simple circuit structure; the gate circuit restores the reverse bias voltage across the detection chip by setting a gate window signal, effectively reduces the recovery time of the detector, overcomes the shortcomings of the conventional passive circuit, improves the detection efficiency of the device, and improves the reliability and stability thereof;

[0097] S40: The output delay module measures the rising edge time of the avalanche pulse signal through a double-threshold front edge recognition technology, compares it with a "standard" avalanche pulse signal, obtains the current pulse output detection delay △t, and sends the delay amount △t to the time compensation module;

[0098] S50: The constant ratio timing module dynamically adjusts the high and low levels according to the amplitude of the measured signal, and takes the fixed proportional point of the signal rising edge as the time discrimination point t2, thereby effectively reducing the drift error of the time discrimination;

[0099] S60: The time compensation module obtains the time jitter △tjitter caused by the change of the to-be-measured pulse waveform according to the relationship between the pulse output detection delay and the time jitter, and corrects t2, thereby accurately compensating the delay drift error caused by the non-constant reverse bias voltage within the gate signal width, and realizing the delay stability of the detector output;

[0100] S70: The temperature compensation module uses semiconductor refrigeration technology to place the APD in a constant-temperature environment lower than room temperature, ensures the stable operation of the APD chip, reduces the dark count, and improves the reliability of the system.

[0101] To solve the above technical problems, the application further provides a satellite laser ranging method, and a system structure thereof is shown in the figure. Figure 13 The satellite laser ranging method comprises the following steps:

[0102] Download the observation target prediction ephemeris on the day of observation, select the observation target, and obtain the azimuth, elevation and distance of the target satellite, etc.

[0103] W10: The telescope is guided by the servo control system to track the target satellite, and after stable tracking, a laser pulse is emitted;

[0104] W20: The synchronization signal of the laser pulse generated by the PIN photodiode is transmitted to the constant fraction discriminator (CFD), and the main wave signal is output into the time timer A channel, and the control system records the main wave time;

[0105] W30: The photons reflected back from the target satellite are converged to the low time jitter APD target surface through the receiving telescope, and the echo signal is generated, and the echo signal is transmitted to the time timer B channel, and the echo time is recorded. The difference between the main wave time and the echo time is the distance between the star and the ground;

[0106] Among them, the photons reflected back from the target satellite are converged to the low time jitter APD target surface through the receiving telescope and generate the echo signal, and the echo signal is transmitted to the time timer B channel and the echo time is recorded.

[0107] W31: When the reverse overvoltage is 5V, the APD output pulse signal waveform is a "standard" avalanche pulse signal, and the rise time and time jitter of the pulse are obtained by using semiconductor numerical simulation technology; wherein the pulse rising edge time △t0 refers to the time required for the pulse to rise from 10% of the amplitude to 90% of the amplitude, that is, the detection delay △t0 of the "standard" avalanche pulse signal;

[0108] W32: Obtain the APD output pulse signal waveform under different reverse overvoltage, as shown in Figure 14 When the overvoltage is 15V, the avalanche pulse output delay is 30ps, and the time jitter difference caused is 190ps;

[0109] W33: The passive gating circuit module receives the gating instruction, at t1, the sum of the gating pulse signal amplitude voltage 20V provided by the passive gating quenching circuit module and the bias voltage 80V provided by the high voltage bias module is greater than the avalanche voltage 83V of the detection chip, as shown in Figure 15 At this time, the gate is opened, and the APD is in the Geiger mode, which can detect single photon signals;

[0110] W34: The input light module outputs single photon level measured light to the detection chip, and the valence band electrons absorb photon energy to jump to the conduction band, and avalanche multiplication occurs under the action of the applied reverse bias, forming an avalanche current;

[0111] W35: The output delay module uses dual-threshold leading-edge recognition technology to measure the rising edge time of the avalanche pulse signal and compare it with the "standard" avalanche pulse signal to obtain the current pulse output detection delay △t, and sends this delay △t to the time compensation module;

[0112] W36: The constant ratio timing module dynamically adjusts the level according to the amplitude of the measured signal, using a fixed ratio point on the rising edge of the signal as the time discrimination point t2, effectively reducing the drift error of the time discrimination;

[0113] W37: The time compensation module assumes a linear relationship between pulse detection delay Δt and time jitter Δtjitter. It converts a 1ps positive pulse detection delay into a 6ps negative time shift, capturing the time jitter Δtjitter caused by variations in the measured pulse waveform. It then automatically corrects t2, accurately compensating for delay drift errors caused by non-constant reverse bias voltage within the gate signal width. The corrected echo signal is then transmitted to channel B of the timer. Simultaneously, the passive gating circuit module quenches the avalanche signal of the detection chip through a passive circuit, completing the APD photoelectric signal conversion.

[0114] W38: The temperature compensation module uses semiconductor refrigeration technology to place the detection chip in a constant temperature environment below room temperature, ensuring the stable operation of the detection chip, reducing dark counts, and improving system reliability.

[0115] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A low-time-jitter single-photon detection system, characterized in that: include: Input optical module, used to output the measured light at the single-photon level to the detection chip; A high-voltage bias module, used to apply a reverse bias voltage to the detection chip; A detection chip, used to receive incident light signals and convert them into current signals; Temperature control module, used to maintain constant operating temperature of the detection chip; Passive gated quenching circuit module, used to quench the avalanche pulse signal generated by the detection chip and restore the bias voltage at both ends of the detection chip; Output delay measurement module, used to measure the detection delay Δt between the avalanche pulse signal and the standard avalanche pulse signal; Constant ratio timing module, used to identify the echo time and eliminate echo jitter caused by different signal amplitudes; and The time compensation module is used to compensate for the drift error caused by the detection delay Δt and output the compensated echo reception time; The passive gated quenching circuit module quenches the avalanche signal of the detection chip through a passive circuit and restores the bias voltage at both ends of the detection chip through a gated circuit. The passive circuit achieves automatic quenching through a high-impedance suppression resistor voltage divider; the gated circuit uses a set gated window signal to restore the reverse bias voltage at both ends of the detection chip. The output delay measurement module measures the rising edge time of the avalanche pulse signal through the dual-threshold leading edge recognition technology, compares it with the standard avalanche pulse signal, obtains the current pulse output detection delay Δt, and sends the detection delay Δt to the time compensation module; The time compensation module assumes a linear relationship between the pulse detection delay Δt and the time jitter difference Δtjitter, converts a 1ps positive pulse detection delay into a 6ps negative time shift, obtains the time jitter difference Δtjitter caused by the change in the pulse waveform to be measured, and automatically corrects the moment judgment point t2 to accurately compensate for the delay drift error caused by the non-constant reverse bias voltage within the gate signal width. Finally, the corrected echo signal is output.

2. A method for detecting single photons with low temporal jitter, characterized in that: The low-time-jitter single-photon detection method comprises the following steps: The input optical module is used to output the measured light at the single-photon level to the detection chip. The electrons in the valence band absorb the photon energy and transition to the conduction band. Under the action of an external reverse bias, avalanche multiplication occurs, forming an avalanche current. The high-voltage bias module provides the APD with a reverse bias voltage V0 that is slightly lower than the avalanche voltage. At time t1, the sum of the gate pulse signal amplitude voltage V1 provided by the passive gate quenching circuit module and the reverse bias voltage V0 is greater than the avalanche voltage V' of the detection chip. At this time, the gate is open and the APD is in Geiger mode, which is used to detect single-photon signals. The passive gated quenching circuit module quenches the avalanche signal of the detection chip through a passive circuit, and the gated circuit restores the bias voltage at both ends of the detection chip; the passive circuit achieves automatic quenching through high-impedance suppression resistor voltage division; the gated circuit uses the set gate window signal to restore the reverse bias voltage at both ends of the detection chip; The output delay module measures the rising edge time of the avalanche pulse signal through the dual-threshold leading-edge recognition technology, compares it with the standard avalanche pulse signal, obtains the current pulse output detection delay Δt, and sends the detection delay Δt to the time compensation module; The constant ratio timing module dynamically adjusts the level according to the amplitude of the measured signal, and takes the fixed ratio point of the rising edge of the signal as the time judgment point t2; By assuming that the pulse detection delay Δt is linearly related to the time jitter difference Δtjitter, the time jitter difference Δtjitter caused by the change in the measured pulse waveform is obtained, and t2 is corrected to accurately compensate for the delay drift error caused by the non-constant reverse bias voltage within the gate signal width; The temperature compensation module uses semiconductor refrigeration technology to place the APD in a constant temperature environment below room temperature.

3. A satellite laser ranging method, characterized in that: The method for satellite laser ranging comprises the following steps: Download the forecast ephemeris of the observation target for the day, select the observation target, and obtain the azimuth, altitude and distance information of the target satellite; The servo control system guides the telescope to track the target satellite and emits laser pulses after stable tracking; The synchronization signal of the laser pulse generated by the photodiode is transmitted to the constant ratio discriminator and outputs the main wave signal into the time timer A channel. The control system records the main wave moment; The photons reflected from the target satellite are focused on the target surface of the low-time-jitter APD through the receiving telescope, generating an echo signal. The echo signal is then sent to the B channel of the timer to record the echo time. The difference between the main wave time and the echo time multiplied by the speed of light is the distance between the satellite and the ground. Among them, the photons reflected from the target satellite are converged to the low time jitter APD target surface through the receiving telescope and generate echo signals, and the echo signals are transmitted to the time timer B channel, and the echo time is recorded, including the low time jitter single photon detection method as described in claim 2.

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